The present invention relates, in general, to multi-colored lustrous pearlescent pigments.
Along with gem stones (e.g., diamond, ruby, emerald, topaz, opal, jade), and precious metals (e.g., gold, silver, platinum), pearls are among the most prized possessions (or luxury items) for human beings for millenniums. Beside their natural beauty, the brilliant color and luster, they are often associated with social status and level of well-being. As a result, and not surprisingly, the trend of cosmetics makeup is to emulate or recreate these “natural” and “aesthetic” appearances of pearl, gem and precious metals with less expensive materials such as interference pigments (e.g., metal oxide coated mica). The most common types of pearlescent pigments are micronized titanium dioxide, metal oxide coated mica, metal oxide coated alumina, metal oxide coated silica, basic lead carbonate, bismuth oxychloride, and natural fish silver.
Metal oxide coated mica pigments are characterized by excellent optical, chemical, mechanical, toxicological, and environmental properties. Natural or synthetic mica, and alternative supports, such as aluminum flakes, or SiO2 platelets, can be used alone, or as a support for titanium dioxide, iron oxide (Fe2O3 or Fe3O4), iron ferrocyanide (Iron Blue or Prussian Blue), tin oxide, and chromium oxide. The color space defined by these coated mica-based pigments is based on the type of coating (e.g. metal oxide, colorant, etc.) used, the layer thickness, and the number of coated layers.
Among the natural pearls, the most expensive are black pearls, which come with various undertone and color flops. To faithfully emulate this aesthetic optical effect in cosmetic makeup is one of the top challenges facing a cosmetic pigment maker and formulator. The traditional approach to these pigments is to blend dark solid-color inorganic pigment (e.g., carbon black) with white platy pearlescent pigments (e.g., TiO2 coated mica, TiO2 coated borosilicate, TiO2 coated alumina). The platy interference pigment provides the luster, brilliance (reflection), transparency and depth of field. The solid-color pigment(s) provide(s) the dark undertone and surface coverage. However, this type of blend usually appears to be much “dirtier”, “lack luster”, and “lack transparency” compared to the natural pearl. The primary reason for that is fouling of the smooth surface of white pearlescent pigment by the solid-color pigment granules, which leads to light scattering and disruption of light interference.
Metal oxide coated platelet pigments may be magnetic or exhibit magnetic susceptibility. When placed into a liquid coating, regions of the coated pigment may be aligned by an externally applied magnetic field and produce a goniochromatic, or angle dependent optical effect. This effect may be used to create an impression of a two- or three-dimensional image. After the pigments have been aligned, the coating may be cured to solidify the optical effect. Examples of pigments and methods of aligning them are discussed in U.S. Pat. Nos. 6,589,331, 6,902,807, 5,223,360, 6,759,097, and 7,258,900. However, the magnetic pigments are significantly limited in terms of color space. The typical colors available are metallic black, grey shades, or bichromic shades characterized by a black or reddish brown absorbance color combined with a weak interference color.
A need exists to expand the existing color space of metal oxide coated pigments to more vibrant, lustrous colored shades, as well as, antique dark pearlescent shades, using a processing method that allows for optimal control of color and opacity. In addition, a need exists for more colorful magnetic pigments that have a larger color contrast between aligned and non-aligned pigments.